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CANDU Reactor

Harry Cape


Mr. Morrison

April 3, 2007

Introduction The CANDU reactor is a Canadian nuclear invention that supplies people around the world with clean electricity. It is one of the safest nuclear reactors built, and has developed many different shut down systems as safety precautions. The CANDU reactor currently supplies fifteen percent of Canada's electricity, and almost half of Ontario's electricity. As energy demands increase constantly, and global warming and climate change threaten the earth, nuclear technology may be the only solution to an increase in electricity production and a decrease in harmful greenhouse gases. History Nuclear energy is a fairly new concept. It began in 1939 with the discovery of nuclear fission (Whitlock, 2007). In 1942 Canada and Great Britain created a secret lab at the University of Montreal where heavy water, which was moved from England because of the war, was stored (Whitlock, 2007). According to Whitlock (2007), the United States of America joined the program to begin research on an atomic bomb, but would later leave the program to do testing alone. With the United States gone, Canada and Great Britain focussed more on the use of deuterium oxide, heavy water, rather than atomic weapons (Whitlock, 2007). After the war ended in 1945, Canada began looking into nuclear energy's peaceful uses (Whitlock, 2007). Whitlock (2007) stated that in the 1950s nuclear power caught the public's attention and its uses as a source of electricity were deeply looked into. Canada's first nuclear power reactor was CANDU (Whitlock, 2007), an acronym for CANada Deuterium Uranium (CANDU, nd; CANDU reactor, 2007). CANDU is the only nuclear power plant found in Canada, supplying fifteen percent of its electricity (CANDU, nd; Whitlock, 2007). Advancements One of the major advancements of the CANDU system is that it does not need to be shut down for refuelling like in light water reactors (CANDU Reactor, 2007; Whitlock, 2007). Because of this ability, CANDU generally has high performance ratings (CANDU Reactor, 2007; Whitlock, 2007). According to Whitlock (2007), the ability to remove fuel while the reactor is running allows defective fuel to be detected and removed quickly (Whitlock, 2007). In order to remove fuel cells two identical machines, with the ability to insert or discard fuel bundles, are put on either side of the calandria (Whitlock, 2007). Theses devices are controlled by remote in a control room (Whitlock, 2007). Used uranium bundles are discarded in a storage facility (Whitlock, 2007). CANDU Reactor Plants CANDU was developed through a partnership between Atomic Energy of Canada Limited (AECL), Hydro-Electric Power Commission of Ontario, and Canadian General Electric (GE Canada) (CANDU reactor, 2007). There are currently twenty-nine reactors around the world, on four different continents and in five countries (CANDU, nd). According to Whitlock (2007) and "CANDU reactor" (2007) all nuclear power in Canada is produced by CANDU. There are eighteen reactors in Canada, two in refurbishment and six decommissioned. Four reactors are in South Korea, two in China, two in India, one in Argentina, one in Romania, and one in Pakistan (CANDU reactor, 2007; Whitlock, 2007). There are a further eleven CANDU "derivatives" in India, which are based on the

CANDU design but are not official CANDU reactors. This is because Canada stopped nuclear trading with India when they set off a nuclear bomb (CANDU reactor, 2007; Whitlock, 2007). The science The CANDU reactor uses two key substances, deuterium oxide, also known as heavy water, as the coolant and uranium as the fuel (CANDU, nd). According to Whitlock (2007), unlike light water, H2O, deuterium oxide replaces the hydrogen atom with heavy hydrogen, or deuterium, to become D2O (Whitlock, 2007). The reason heavy water is used is because it is eight times worse than light water at slowing down neutrons, and absorbs 600 times less than light water (Whitlock, 2007). This key difference allows CANDU to use natural uranium and still reach criticality (Whitlock, 2007). Since light water only allows refined uranium to reach criticality, using heavy water saves the cost of extra uranium refining (Whitlock, 2007). According to Whitlock (2007), uranium mining is done entirely in Northern Saskatchewan. The uranium is then separated from the rest of the rock and sent to a refinery to reduce the uranium to uranium trioxide to be used in the reactor (Whitlock, 2007). The uranium trioxide is than reduced to uranium dioxide, a black powder that is made into cylindrical pellets about a centimetre in diameter and length (Whitlock, 2007). These pellets are put into tubes made of zircaloy, fifty centimetres long (Whitlock, 2007). The tubes are welded shut and put into CANDU (Whitlock, 2007). A standard CANDU reactor holds thirty-seven tubes, each one weighing about twenty kilograms (Whitlock, 2007). How it works In order for the nuclear reactor to work, fission must occur. Fission will only happen in just the right circumstances (CANDU Reactor, 2007). A calandria with horizontal tubes is filled with uranium bundles (CANDU, nd). Six to ten are switched every day (Whitlock, 2007). The calandria is then filled with heavy water (CANDU, nd). Fission releases energy is the form of heat. This heat is used to heat up more heavy water (CANDU, nd; Whitlock, 2007). The steam from the heavy water is used to heat light water which creates steam to turn electrical turbines (CANDU, nd; CANDU Reactor, 2007; Whitlock, 2007) In one to one and a half years the uranium fuel runs out and is replaced (CANDU Reactor, 2007). Used uranium is put in a tank of water which cools the fuel bundles and absorbs the radiation (CANDU Reactor, 2007). According to Whitlock (2007) two independent computers are used to control the reactor. Both run at the same time, but one is only used as a back up. CANDU variations There are a few variations of the CANDU reactor that range from 125 megawatts of energy to over 900 megawatts of energy (Whitlock, 2007). The differences are the fuel channels (Whitlock, 2007). The CANDU 6 version produces about 700 MWe, while the CANDU 9 produces 900 MWe (Whitlock, 2007). According to Whitlock, the AECL is working on a new Advanced CANDU Reactor, ACR, that would be smaller, more efficient, use light water and less heavy water to lower costs, use some slightly enriched uranium to extend fuel life three times, have an increased power, and be less costly to construct.

Accidents Since the creation of CANDU, there have been two accidents but no civilian injuries. The first was on December 12, 1952 at the Chalk River NRX (Whitlock, 2007). A human error caused the power to surge for a minute, melting and breaking the fuel rods. A mechanical malfunction in the shut off roads made it so the reactor did not shut off (Whitlock, 2007). The radioactive waste was carried by millions of gallons of cooling water into the basement of the reactor, and was then pumped to waste management facilities were the water was monitored to meet safety requirements (Whitlock, 2007). The calandria was severely damaged, but there were no casualties (Whitlock, 2007). According to Whitlock, a massive clean up took place involving the Canadian and American Military and AECL staff. The positive to this accident was that it taught Canada an important lesson. It showed the need for fast acting shut down systems and a high level power threshold (Whitlock, 2007). The NRX was completely rebuilt and was operating within 14 months (Whitlock, 2007). The second accident happened May 24, 1958 at the Chalk River NRU (Whitlock, 2007). It was caused by a fuel handling accident and was not as serious as the previous one. The accident occurred when the system was shut down to remove failed fuel (Whitlock, 2007). According to Whitlock, the fuel rod was not cool enough and began to burn. The rod broke apart while being moved to storage and a piece fell on the maintenance bridge and continued burning (Whitlock, 2007). The fire was quickly extinguished by staff, but the building was contaminated. Clean up began soon after, and the plant was running that August. The impact of CANDU The CANDU reactor has many economical and environmental advantages. First of all, a new CANDU power plant would supply jobs for 30,000 people, and would collect $700 million of tax to be used to improve other affairs (CANDU, nd). CANDU currently supplies fifteen percent of Canada's energy (CANDU, nd; Whitlock, 2007). According to Whitlock (2007), in 1997 CANDU produced almost half of Ontario's energy. CANDU is also cost efficient because it does not need uranium to be intensely refined in order to reach criticality (CANDU reactor, 2007). According to Whitlock, every year $1 billion is saved in Canada by not using foreign energy. A total of $34 billion have been saved between 1962 and 1994. Also according to Whitlock, selling two CANDU reactors abroad creates $760 million dollars for Canada, 10,000 jobs, and business for 1,500 private companies. In 2000, exporting by the nuclear industry created $1 billion (Whitlock, 2007). The environment would also experience many benefits from CANDU. Without nuclear technology for forty years, 2 billion tonnes of carbon dioxide, 11 million tonnes of sulphur dioxide, and 2.5 million tonnes of nitrogen oxides would be let into the Earth's atmosphere (CANDU, nd). Nuclear energy is much cleaner than fossil fuels because there is no ash, gas, or airborne particles created (Whitlock, 2007). According to Whitlock, a twenty kilogram bundle of uranium can supply 100 homes with electricity for one year. The same amount of energy is created from 400 tonnes of coal, 270,000 litres of oil, or 3 million litres of natural gas (Whitlock, 2007). Whitlock also said that 1 kilogram of pollution is avoided for every kilowatt per hour generated by nuclear energy. Studies

show that 20 to 100 deaths are caused by pollution from coal for every gigawatt of energy generated per year (Whitlock, 2007). This adds up to 300 to 1,600 deaths in Canada alone. CANDU would have than saved between 4,000 and 20,000 lives since its creation (Whitlock, 2007) Safety There are four main aspects that allow CANDU to prevent accidents. They are redundancy: having more than one way to do something, diversity: more than one way to operate something, separation: dividing the systems, and protection: follow regulations (Whitlock, 2007). The building containing the reactor is made of concrete walls one metre thick, and coolants are kept in a giant concrete structure (CANDU Reactor, 2007). No one is allowed to live in a one kilometre radius of the reactor (CANDU Reactor, 2007). The CANDU set up takes human error, equipment failure, natural disasters, and attacks into consideration (CANDU, nd). There are two ways to shut down the reactor within two seconds (Whitlock, 2007). The first, SDS 1, drops rods into the core to stop fission (Whitlock, 2007). The second, SDS 2, injects a liquid poison into the reactor to stop fission (Whitlock, 2007). Other reasons for high safety are that a low temperature moderator is used, a slower kinetics is used with heavy water, and defective fuel can be detected (Whitlock, 2007). Radiation Radiation is a big concern among the public when they think of nuclear energy. However, Canada has very strict regulations on nuclear power plants. According to Whitlock (2007), CANDU does emit air and water radiation, but only to Canadian regulations. These rules allow Canadians to receive only about one third more radiation than a normal person would (Whitlock, 2007). That amount is about 700 times less than what could have a health effect (Whitlock, 2007). Scientists There have been many scientists that have helped in the development in Canada's nuclear reactor. Some are born in the country and others from abroad. They have all contributed to the success of CANDU with their designs, plans, and effort, as well as their expertise, and knowledge on nuclear energy. They are the beginnings of CANDU, as well as the ones who improve it to make it an even superior reactor. It is because of these people that Canadians and others around the world have their current quality of life. The following will introduce three key figures in the development of CANDU. Harry Thode Harry Thode was born in Dundurn, Saskatchewan and attended the University of Saskatchewan (Murray, 1991). He took chemistry and physics (Murray, 1991). Thode was a pioneer in nuclear research and was highly involved with the atomic energy project in Montreal, Québec. He worked on the use of atomic energy in war (Murray, 1991). Thode worked with Harold Urey, the discoverer of deuterium oxide (Murray, 1991). Thode built Canada's first mass spectrometer, a machine that measures the mass of isotopes (Murray, 1991). Thode worked on uranium fission and allowed the CANDU reactor to exist (Murray, 1991).

Wilfrid Bennett Lewis Wilfrid Bennett Lewis was a nuclear physicist who worked on nuclear energy development for almost fifty years (Johnson, nd). He was born in Cumberland, England on June 24, 1908 (Johnson, nd). Lewis went to Cavendish Laboratory where he earned a doctorate (Fawcett, nd). He continued his nuclear research there until 1939 (Fawcett, nd). Lewis agreed to come to Canada to work on the research at Chalk River, and stayed there for 27 years (Fawcett, nd). He came in September 1946, when he was 38, and became the Director of Atomic Energy Research at the Chalk River site (Fawcett, nd Johnson, nd). Lewis directed the Canadian nuclear research program from 1946 to 1973 (Johnson, nd). He worked on the use of particle accelerators for nuclear reactions (Johnson, nd). In 1952, Lewis became vice-president of research and development for the AECL (Fawcett, nd; Johnson, nd) and in 1963 he became senior vice-president of Atomic Energy Canada Limited (Johnson, nd). Lewis worked on what would become CANDU (Johnson, nd). It was his idea to make the calandria horizontal rather that vertical, which allowed for loading while the reactor is running (Johnson, nd). Lewis served twenty-one years on the International Atomic Energy Agency's Scientific Advisory Committee and was the Canadian representative to the United Nations Scientific Advisory Committee (Johnson, nd). Lewis received the Enrico Fermi award from the United States department of energy (Johnson, nd). It is because of Wilfrid Bennett CANDU is what it is today (Fawcett, nd). Gordon Brooks Gordon Brooks was born in Edmonton, Alberta on November 4, 1930 (Gordon Brooks, 1992). Brooks graduated the University of Alberta in Chemical engineering (Gordon Brooks, 1992). He moved to Deep River, Ontario, to work at the Chalk River labs (Gordon Brooks, 1992). Brooks also worked at the Sheridan Park Research Centre (Gordon Brooks, 1992). Brooks was the first General Manager of Power Projects in Montreal and built the Gentilly-1(Gordon Brooks, 1992), a light water coolant nuclear reactor prototype that demonstrated the advantage of using heavy water as the coolant rather than light water (Whitlock, 2007). Brooks retired in 1991 as the CANDU Operations Vice President and Chief Engineer (Gordon Brooks, 1992). CANDU (nd). CANDU: Canada's Nuclear Energy Source. Retrieved February 22 from CANDU Reactor (2007). In The Canadian Encyclopedia. Retrieved February 22, 2007 from SEC825457 CANDU reactor (2007, February 18). In Wikipedia, The Free Encyclopaedia. Retrieved 01:37, February 23, 2007, from Fawcett, R. (nd) Nuclear Pursuits. Retrieved March 8, 2007 from Johnson, C. (nd) Half a Century of Nuclear Pioneering. Retrieved March 8, 2007 from

Murray, G. (1991) Dr. Harry Thode: Quiet Man of Science. Retrieved March 8, 2007 from Personality of the Year: Gordon Brooks (1992) Retrieved March 8, 2007 from Whitlock, J. (2007, February 15). In Canadian Nuclear FAQ. Retrieved February 22, 2007 from


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